Tackling crosswords and puzzles can help 80-year-olds to retain the brain-power of a 70-year-old and even delay dementia by keeping the mind sharp, researchers believe.

A study looking at the benefits of brain training found nearly three quarters of those who took part displayed cognitive benefits a decade on.

Researchers said the findings were "pretty astounding." Previous studies have demonstrated benefits of keeping the brain active later in life, but this is the first of its kind to show how a little training goes a long way.

The 10-year U.S. study involved 2,800 participants, the largest of its kind so far, with an average age of 74.

Participants were split into four groups: some received brain training focusing on processing speed, others on memory and others on reasoning ability. A fourth group did not get any brain training.

All four groups were given 10 sessions lasting 60 to 70 minutes over five or six weeks and nothing else for the next decade. The effects were measured at intervals over the next 10 years. Results showed that around 60 per cent of those who participated in the brain drills said they had less difficulty with day-today activities such as shopping and handling their finances, compared to 49 per cent of those who did not have the training.

George Rebok, an expert on aging and a professor at Johns Hopkins University in Baltimore, said: "What we found was pretty astounding. Ten years after the training, the effects were durable for the reasoning and the speed training."

Sharon Tennstedt, vice-president of New England Research Institutes and co-author of the study, said: "If training can have that kind of effect on preserving cognitive function, then there is potential for delaying dementia or attenuating it."

Previous research has found a lower risk of Alzheimer's among people who often go to the theatre, read or play games. Going to a museum, dancing and playing an instrument had a positive effect, as did regular social interaction.